Frank Madafferi, Tony's brother, was granted a visa after the lobbying of several MPs.

Security sources said the work-experience placement was a major security lapse.

Confidential Italian justice department documents reveal that in the years before his son's 2010 work placement, the Adelaide-based Mafia godfather was under investigation for importing drugs to Australia from Europe.

The Australian embassy is the conduit for a stream of sensitive information between Italian and Australian authorities about the Mafia's activities.

Police in Rome had, in late 2007, also tracked the godfather through the city with a local Mafia boss called Francesco Frisina.

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There is no evidence that the embassy placement, which involved the man's son working briefly in a clerical role, led to any security breaches, but security sources have described it as a major lapse.

A spokesman for the Department of Foreign Affairs and Trade said the son "assisted with managing events and provided administrative support services ... [He] did not have access to sensitive information during his internship".

It is also a further embarrassment for the then ambassador to Italy, Amanda Vanstone, who already faces questions over her decision as immigration minister in the Howard government to give a visa to another Mafia boss, Frank Madafferi.

Ms Vanstone has said that decision was made on humanitarian grounds about the impact of deportation on Madafferi's family. But it came after police warnings Madafferi was a violent criminal who posed a major risk to the community. Ms Vanstone's predecessor, Philip Ruddock, had previously ordered Madafferi's deportation because of his lengthy and serious criminal record.

There is no suggestion Ms Vanstone acted improperly in either case, though confidential police assessments suggest it indicates that her South Australian Senate office had probably been infiltrated by Mafia figures.

Police suggest this occurred under the guise of legitimate activities and without Ms Vanstone's knowledge.

Mafia figures and their associates "are likely to have ingratiated themselves with her office and that through their legitimate public face were capable of achieving influence", according to a 2013 law enforcement assessment held by several state policing agencies.

Ms Vanstone did not respond to repeated messages sent via email and phone.

The revelations are part of a year-long investigation by Fairfax Media and Four Corners into the Calabrian Mafia's Australian operations.

The Adelaide Mafia godfather cannot be named for legal reasons, but is an associate of several other Mafia figures who have built links to both the Liberal and Labor parties.

Security sources said the work experience placement was a major security lapse, and questioned how the crime figure's son obtained it given Australia's National Crime Authority had documented his father's alleged involvement "in the importation of illegal drugs [and] strong links with Italian organized crime identities."

An Italian police file shared with the Australian embassy states the Australian godfather is part of an "Australian sub-group of 'Ndrangheta [Calabrian mafia] operatives with links to Calabria and also the US and Canada [conducting] activities related to the movement of drugs internationally."